How to save every drop of insulin with tslim pump?

I have a tandem tslim pump, and i recently learnt that there are around 40 units left in the cartridge and tubing after changing them. I know how to use syringe to suck out the 25 units from the cartridge. How do i suck out the rest from the tubing?

The trainer for my Medtronic Pump said that one of the reasons for changing the reservoir and infusion set, is to throw away the old insulin. Your pump is probably very close to your body, and thus at a temperature that causes the insulin the go bad in a few days.